1. Field of the Invention
The present invention relates generally to a novel and improved resin reinforced expansion anchor system that utilizes a specially configured, thin-walled expansion shell together with a thin-walled, dual-taper plug for expanding the shell, wherein the shell and the plug cooperate to implement a particularly desirable type of mechanical expansion anchoring action while simultaneously providing a symmetrical array of resin flow passages at circumferentially spaced locations about the anchor assembly to permit proper distribution and flow of a quick setting resin mix as a relatively large diameter rock bolt or threaded bar is being securely anchored in a blind drilled hole of relatively small diameter, with the anchoring action of the mechanical expansion anchor assembly being desirably augmented by the anchoring action of a concurrently established resin bond. More specifically, the system of the present invention provides a means for effecting combined mechanical expansion anchoring and resin bond anchoring of a relatively large diameter threaded member such as a 7/8" rock bolt in a relatively small diameter hole such as a 1 3/8" blind drilled hole.
2. Prior Art
In mine work, such as coal mining, and in tunnel and excavation work, often it is necessary to reinforce and support roof and/or wall formations to prevent rock falls or cave-ins. The needed reinforcement and support typically is provided (1) by drilling a spaced array of blind holes into the roof and/or wall formations that are to be supported, (2) by installing elongate bolts or bars into the blind drilled holes (with each of the bolts or bars being inserted into a separate one of the drilled holes), (3) by "anchoring" the bolts or bars in place in their respective blind drilled holes, and (4) by utilizing such portions of the bolts or bars as project out of the blind drilled holes to connect with and clampingly retain support plates in place against such roof and/or wall formations as require reinforcement and support.
The "anchoring" of end regions of bolts or bars that are inserted into blind drilled holes typically is effected either (1) by utilizing mechanical anchor assemblies that are threaded onto the end regions of the bolts or bars, and that are expanded in situ to rigidly connect the bolts or bars to rock formations that define the side walls of the blind drilled holes, or (2) by utilizing a quick setting resin, the components of which are mixed in situ in the blind drilled holes, and that is distributed immediately upon being mixed so as to flow about outer surface portions of the bolts or bars and about inner surface portions of the blind drilled holes to establish what is referred to as "resin bond anchoring" between the bolts or bars and their surrounding rock formations.
The diameter of a blind drilled hole that is formed in a mine roof or the like to receive a rock bolt or a reinforcing bar that is to be anchored in the hole depends in large part on the character of the anchoring system that is to be employed. When a mechanical expansion anchor assembly is to be used, the diameter of the blind drilled hole must take into account both the minimum diameter that will permit free insertion of the anchor assembly into the hole, and the maximum diameter with which the expansion anchor assembly can safely be deployed. If the drilled hole is too small in diameter, installation problems arise inasmuch as the expansion anchor assembly cannot be inserted with ease into the drilled hole. If the drilled hole is too large in diameter, the expansion anchor assembly cannot properly anchor to rock formations that surround the hole. When a resin bond anchoring system is to be used, the diameter of the blind drilled hole is preferably kept relatively small so that a reasonable quantity of expensive resin material inserted into the hole will effect proper anchoring of a rod or bar to surrounding rock formations.
When, for example, a rod or bar having a nominal 7/8" diameter is to be anchored in a blind drilled hole formed in a mine roof, use of an expansion anchor assembly typically will require the drilling of a hole having a diameter of 1 1/2", 1 5/8" or 1 3/4" depending on the character of the expansion anchor assembly that is selected for use. However, if resin bond anchoring is to be used, a hole diameter of 1 1/8", 1 1/4" or 1 3/8" normally would be selected, with one of the smaller of these hole diameters being chosen when use of expensive bonding resin must be kept to a minimum, and with one of the larger hole diameters being chosen when there is a need to maximize the surface area of contact between the bonding resin and the rock formations that surround the blind drilled hole.
While proposals have been made to utilize resin bond anchoring in combination with mechanical expansion anchoring to reinforce or otherwise strengthen or complement the anchoring of a bolt or bar in a drilled hole, a problem that has tended to limit the use in combination of these two types of anchoring systems has been the large quantities of expensive resin that are needed to properly fill the relatively large diameter holes that are characteristically used with mechanical expansion anchor assemblies. Thus, the need has been recognized to provide mechanical expansion anchor assemblies that require the drilling of smaller diameter holes in mine roofs and the like so that, if resin bond anchoring is to be used in combination with mechanical expansion anchoring, less expensive quantities of bonding resin will suffice to effect the desired resin bond anchoring.
Combined use of mechanical expansion anchoring with resin bond anchoring has proved to be advantageous in applications where neither of these different types of anchoring used alone is found to provide a fully satisfactory anchor, and where neither of these types of anchoring are found to interfere with proper operation of the other. Stated in another way, the very different characteristics of these contrasting types of anchoring systems often can be used to advantage to augment or complement each other, so long as the associated conditions of use are not such as to cause the operation of one of the types of anchoring to interfere with proper operation of the other.
An example of an application wherein combined use of mechanical expansion anchoring and resin bond anchoring often is desirable, but where a combination of the two types of anchoring systems has led to interference of one with the proper operation of the other, arises when a relatively large diameter rock bolt or threaded bar needs to be anchored in a relatively small diameter blind drilled hole. Such a situation presents a problem in that there is relatively little clearance between the outer diameter of the threaded bolt or bar and the interior of the drilled hole, whereby a mechanical expansion anchor assembly that is threaded onto a bolt or bar and is expanded to anchor the bolt or bar tends to fill the majority of the available space, thus leaving neither adequate space nor flow paths for positioning and distribution of resin. A particularly difficult problem arises when a rock bolt or threaded bar having a relatively large nominal diameter of 7/8" needs to be securely anchored in a blind drilled hole having a relatively small nominal inner diameter of 1 3/8". If an expansion anchor of conventional design is to be used in such an application, the material that forms the relatively movable components of the anchor occupies substantially all of the available space between the outer diameter of the bolt or bar and the inner diameter of the drilled hole. Resin bond reinforcement of an expansion anchor in such an installation is rendered extremely difficult by virtue of the fact that the material which forms the components of the expansion anchor assembly fills or otherwise blocks off substantially all of the available space between the bolt or bar and the walls of the blind drilled hole, whereby adequate space and flow paths for positioning and distribution of resin in order to effect a proper resin bond anchoring action cannot be relied upon to be present.
Stated in another way, conventionally configured expansion anchor assemblies have not proved adequate for use in securing relatively large diameter rock bolts or bars (e.g., 7/8" diameter) within blind drilled holes of relatively small diameter (e.g., holes having inner diameters of 1 3/8"), the reason being principally that the material that comprises the relatively movable components of the expansion anchor assemblies tends to fill, block and/or obstruct spaces and flow paths that are needed within the blind drilled holes in order for resin to achieve a proper anchoring effect. Thus, conventionally configured expansion anchor devices have been found to interfere with proper mixing, positioning and flow of resin when attempts have been made to use conventionally configured mechanical expansion anchors in combination with resin bond anchoring to anchor some relatively large commercially available sizes of rock bolts or threaded bars in relatively small diameter blind drilled holes, with particularly difficult problems being encountered in instances where bolts or bars of a nominal 7/8" diameter need to be anchored securely in blind drilled holes having nominal 1 3/8" diameters.